The former X Factor champ will help out judges Nicole Scherzinger and Simon Cowell in one of the upcoming episodes.
Other artists and industry experts appearing will be singer Ella Eyre & producer Naughty Boy.
Free tickets to be in the audience for filming in Birmingham are available from ApplauseStore here.
Filming takes place at Resorts World Arena in Birmingham.
The minimum age limit is 8+ with those under 18 needing to be accompanied by an adult.
A source told The Sun newspaper about Leona joining the show: “Simon appreciates Leona is a huge part of The X Factor, so getting her on board for his new show brings a sense of continuation.
“She’ll use her industry knowledge and eye for talent to find stars for the girl and boybands.”
It comes after claims that Louis Walsh had turned down an "advisor" role after being told he wouldn't be a judge.
A source claimed: "[Simon] felt it would make more sense to have him mentoring the boys and Nicole looking after the girls. Louis was offered a role as an adviser.
“But it soon became clear there was no real job, so he turned the offer down.”
Dermot O'Leary will return to host the brand new series which was only announced last month.
The show will air over four episodes from Monday, December 9 at 8:30PM on ITV.
The series will then continue on Wednesday, December 11 and Friday, December 13 before a live final on Sunday, December 15 at 8PM.